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What is the Wash?
The Quality of our Water

100-Year Storm Event

On July 8, 1999, the Las Vegas Valley experienced a 100-year storm event. Although the valley frequently gets flash floods throughout the summer months, this event had a tremendous impact.

The Las Vegas Wash is the single drainage point for the entire valley. This means that all of the stormwater, with the exception of the water absorbed into the soil, must exit the valley through the Wash.

The Wash experiences approximately 150-200 cubic feet per second (cfs) of flow on a typical day. During this event, flows were recorded at approximately 16,000 cfs. The Wash channel widened as much as 300 feet at some points.

flood
Northshore Road after the flood. Notice the muddy water.

The property damage, both public and private, that resulted from this event was substantial. (Public property damage was estimated at more than $20 million). One mobile home actually fell into the Flamingo Wash because of the bank eroding beneath it. There were two deaths during this event. One death was a drowning and the other was in a weather related traffic accident.

When the flows reached the Lake Las Vegas intake pipes (where the Wash flows underneath Lake Las Vegas), there was so much debris being pushed against the grates and the flows were so fast that workers were unable to remove the debris fast enough. As a result, the water flowed up and over, into the lake at Lake Las Vegas. At the other end of the lake, the spillways were hard at work.

At Las Vegas Bay (the location of the confluence of the Las Vegas Wash and Lake Mead) the amount of sediment that entered from the Wash was tremendous.

Due to this storm, we now have a better understanding of how these events affect the banks of the Wash and, therefore, how we should approach stabilizing them. The following chart shows the peak discharges during the event as well as the previous maximum discharges for these locations:

Location
Peak Discharge
Previous Maximum
Duck Creek at Eastern Ave.
4300cfs
I
Duck Creek near Hollywood Blvd.
3100cfs
3000cfs (9/11/98)
Flamingo Wash at Torrey Pines
1100cfs
I
Flamingo Wash at Decatur
3000cfs
4760cfs (8/10/83)
Flamingo Wash at Eastern Ave.
6800cfs
4100cfs (7/20/98)
Flamingo Wash at Nellis Blvd.
5400 cfs
4100cfs (6/10/90)
Tropicana Wash at Swenson
2000cfs
I
Las Vegas Wash near Sahara Ave.
8600cfs
4400cfs (9/11/98)
Las Vegas Wash at Vegas Valley Drive
11000cfs
I
Las Vegas Wash at Lake Las Vegas
16000cfs
9560cfs (9/11/98)

 

Las Vegas Wash Project Coordination Team • 100 City Parkway, Suite 700 • Las Vegas, NV 89106 • (702) 822-3300